1. Field of the Invention
The invention relates to a segmented metal core for an electromagnetic actuator for a control valve of a fuel injector for an internal combustion engine.
2. Background Art
Co-pending patent application Ser. No. 10/208,587, entitled “Fuel Injector For Diesel Engines”, filed by W. Scott Fischer, David Eickholt and Mike Weston on Jul. 30, 2002, now U.S. Patent 6,758,415, which is assigned to the assignee of the present application, discloses an injector assembly for an internal combustion engine, wherein the control valve and valve actuator are formed as a module that is independent of the pump body and the nozzle assembly. The module, the plunger body and the nozzle assembly are arranged in a linear, stacked relationship. The co-pending application is assigned to the assignee of the present invention.
The control valve in the fuel injector of the co-pending application is closed by applying a voltage to a magnetic circuit having a magnetic core inside the control valve body. The magnetic circuit generates a magnetic flux, which draws the control valve and armature toward the magnetic core.
To open the control valve, the magnetic circuit is demagnetized so that a control valve spring can bias the control valve to its open position. Terminating the applied voltage begins the demagnetization process as the magnetic flux lines decay rapidly. When the magnetic flux lines have sufficiently decayed, the control valve spring overcomes the attractive force of the magnetic circuit and opens the control valve.
In the creation of the magnetic flux, eddy currents are induced in the electrically conductive magnetic material. The eddy currents are detrimental to the performance of the of the magnetic core since they contribute to slow response and energy loss by slowing down the demagnification process. Accordingly, it is desirable to minimize the induced eddy currents.
Past solutions to reducing eddy currents in fuel injectors include designing the magnetic core with stacked, thin laminate material and providing grooves or slots in the magnetic poles. The grooves or slots decrease eddy currents by increasing the length and resistance of the eddy current flow path.
Round magnetic cores have many advantages over other shaped cores in the creation of magnetic flux. However, laminate structures cannot effectively be formed into round magnetic cores. Manufacturing magnetic cores having slots, furthermore, creates a multitude of manufacturing issues which lead to increased downtime and maintenance.